DESCRIPTION

Ip6tables is used to set up, maintain, and inspect the
tables of IPv6 packet
filter rules in the Linux kernel. Several different tables
may be defined. Each table contains a number of built-in
chains and may also contain user-defined chains.

Each chain is a list of rules which can match a set of packets. Each
rule specifies what to do with a packet that matches. This is called
a `target', which may be a jump to a user-defined chain in the same
table.

TARGETS

A firewall rule specifies criteria for a packet and a target. If the
packet does not match, the next rule in the chain is the examined; if
it does match, then the next rule is specified by the value of the
target, which can be the name of a user-defined chain or one of the
special values ACCEPT, DROP, QUEUE or RETURN.

ACCEPT means to let the packet through.
DROP means to drop the packet on the floor.
QUEUE means to pass the packet to userspace.
(How the packet can be received
by a userspace process differs by the particular queue handler. 2.4.x
and 2.6.x kernels up to 2.6.13 include the ip_queue
queue handler. Kernels 2.6.14 and later additionally include the
nfnetlink_queue queue handler. Packets with a target of QUEUE will be
sent to queue number '0' in this case. Please also see the NFQUEUE
target as described later in this man page.)
RETURN means stop traversing this chain and resume at the next
rule in the
previous (calling) chain. If the end of a built-in chain is reached
or a rule in a built-in chain with target RETURN
is matched, the target specified by the chain policy determines the
fate of the packet.

TABLES

There are currently three independent tables (which tables are present
at any time depends on the kernel configuration options and which
modules are present).

-t, --tabletable

This option specifies the packet matching table which the command
should operate on. If the kernel is configured with automatic module
loading, an attempt will be made to load the appropriate module for
that table if it is not already there.

The tables are as follows:

filter:

This is the default table (if no -t option is passed). It contains
the built-in chains INPUT (for packets destined to local sockets),
FORWARD (for packets being routed through the box), and
OUTPUT (for locally-generated packets).

mangle:

This table is used for specialized packet alteration. Until kernel
2.4.17 it had two built-in chains: PREROUTING
(for altering incoming packets before routing) and OUTPUT
(for altering locally-generated packets before routing).
Since kernel 2.4.18, three other built-in chains are also supported:
INPUT (for packets coming into the box itself), FORWARD
(for altering packets being routed through the box), and POSTROUTING
(for altering packets as they are about to go out).

raw:

This table is used mainly for configuring exemptions from connection
tracking in combination with the NOTRACK target. It registers at the netfilter
hooks with higher priority and is thus called before ip_conntrack, or any other
IP tables. It provides the following built-in chains: PREROUTING
(for packets arriving via any network interface) OUTPUT
(for packets generated by local processes)

security:

This table is used for Mandatory Access Control (MAC) networking rules, such
as those enabled by the SECMARK and CONNSECMARK targets.
Mandatory Access Control is implemented by Linux Security Modules such as
SELinux. The security table is called after the filter table, allowing any
Discretionary Access Control (DAC) rules in the filter table to take effect
before MAC rules. This table provides the following built-in chains:
INPUT (for packets coming into the box itself),
OUTPUT (for altering locally-generated packets before routing), and
FORWARD (for altering packets being routed through the box).

OPTIONS

The options that are recognized by
ip6tables can be divided into several different groups.

COMMANDS

These options specify the specific action to perform. Only one of them
can be specified on the command line unless otherwise specified
below. For all the long versions of the command and option names, you
need to use only enough letters to ensure that
ip6tables can differentiate it from all other options.

-A, --appendchain rule-specification

Append one or more rules to the end of the selected chain.
When the source and/or destination names resolve to more than one
address, a rule will be added for each possible address combination.

-C, --checkchain rule-specification

Check whether a rule matching the specification does exist in the
selected chain. This command uses the same logic as -D to
find a matching entry, but does not alter the existing iptables
configuration and uses its exit code to indicate success or failure.

-D, --deletechain rule-specification

-D, --deletechain rulenum

Delete one or more rules from the selected chain. There are two
versions of this command: the rule can be specified as a number in the
chain (starting at 1 for the first rule) or a rule to match.

-I, --insertchain [rulenum] rule-specification

Insert one or more rules in the selected chain as the given rule
number. So, if the rule number is 1, the rule or rules are inserted
at the head of the chain. This is also the default if no rule number
is specified.

-R, --replacechain rulenum rule-specification

Replace a rule in the selected chain. If the source and/or
destination names resolve to multiple addresses, the command will
fail. Rules are numbered starting at 1.

-L, --list [chain]

List all rules in the selected chain. If no chain is selected, all
chains are listed. Like every other ip6tables command, it applies to the
specified table (filter is the default).

Please note that it is often used with the -n
option, in order to avoid long reverse DNS lookups.
It is legal to specify the -Z
(zero) option as well, in which case the chain(s) will be atomically
listed and zeroed. The exact output is affected by the other
arguments given. The exact rules are suppressed until you use

ip6tables -L -v

-S, --list-rules [chain]

Print all rules in the selected chain. If no chain is selected, all
chains are printed like ip6tables-save. Like every other ip6tables command,
it applies to the specified table (filter is the default).

-F, --flush [chain]

Flush the selected chain (all the chains in the table if none is given).
This is equivalent to deleting all the rules one by one.

-Z, --zero [chain [rulenum]]

Zero the packet and byte counters in all chains, or only the given chain,
or only the given rule in a chain. It is legal to
specify the
-L, --list
(list) option as well, to see the counters immediately before they are
cleared. (See above.)

-N, --new-chainchain

Create a new user-defined chain by the given name. There must be no
target of that name already.

-X, --delete-chain [chain]

Delete the optional user-defined chain specified. There must be no references
to the chain. If there are, you must delete or replace the referring rules
before the chain can be deleted. The chain must be empty, i.e. not contain
any rules. If no argument is given, it will attempt to delete every
non-builtin chain in the table.

-P, --policychain target

Set the policy for the chain to the given target. See the section TARGETS
for the legal targets. Only built-in (non-user-defined) chains can have
policies, and neither built-in nor user-defined chains can be policy
targets.

-E, --rename-chainold-chain new-chain

Rename the user specified chain to the user supplied name. This is
cosmetic, and has no effect on the structure of the table.

-A, --appendchain rule-specification

Append one or more rules to the end of the selected chain.
When the source and/or destination names resolve to more than one
address, a rule will be added for each possible address combination.

-h

Help.
Give a (currently very brief) description of the command syntax.

PARAMETERS

The following parameters make up a rule specification (as used in the
add, delete, insert, replace and append commands).

[!] -p, --protocolprotocol

The protocol of the rule or of the packet to check.
The specified protocol can be one of tcp, udp, udplite,
icmpv6, esp, mh or the special keyword "all",
or it can be a numeric value, representing one of these protocols or a
different one. A protocol name from /etc/protocols is also allowed.
But IPv6 extension headers except esp are not allowed.
esp and ipv6-nonext
can be used with Kernel version 2.6.11 or later.
A "!" argument before the protocol inverts the
test. The number zero is equivalent to all. "all"
will match with all protocols and is taken as default when this
option is omitted.

[!] -s, --sourceaddress[/mask]

Source specification.
Address can be either be a hostname,
a network IP address (with /mask), or a plain IP address.
Names will be resolved once only, before the rule is submitted to the kernel.
Please note that specifying any name to be resolved with a remote query such as
DNS is a really bad idea.
(Resolving network names is not supported at this time.)
The mask is a plain number,
specifying the number of 1's at the left side of the network mask.
A "!" argument before the address specification inverts the sense of
the address. The flag --src
is an alias for this option.
Multiple addresses can be specified, but this will expand to multiple
rules (when adding with -A), or will cause multiple rules to be
deleted (with -D).

[!] -d, --destinationaddress[/mask]

Destination specification.
See the description of the -s
(source) flag for a detailed description of the syntax. The flag
--dst is an alias for this option.

-j, --jumptarget

This specifies the target of the rule; i.e., what to do if the packet
matches it. The target can be a user-defined chain (other than the
one this rule is in), one of the special builtin targets which decide
the fate of the packet immediately, or an extension (see EXTENSIONS
below). If this
option is omitted in a rule (and -g
is not used), then matching the rule will have no
effect on the packet's fate, but the counters on the rule will be
incremented.

-g, --gotochain

This specifies that the processing should continue in a user
specified chain. Unlike the --jump option return will not continue
processing in this chain but instead in the chain that called us via
--jump.

[!] -i, --in-interfacename

Name of an interface via which a packet was received (only for
packets entering the INPUT, FORWARD and PREROUTING
chains). When the "!" argument is used before the interface name, the
sense is inverted. If the interface name ends in a "+", then any
interface which begins with this name will match. If this option is
omitted, any interface name will match.

[!] -o, --out-interfacename

Name of an interface via which a packet is going to be sent (for packets
entering the FORWARD, OUTPUT and POSTROUTING
chains). When the "!" argument is used before the interface name, the
sense is inverted. If the interface name ends in a "+", then any
interface which begins with this name will match. If this option is
omitted, any interface name will match.

-c, --set-counterspackets bytes

This enables the administrator to initialize the packet and byte
counters of a rule (during INSERT, APPEND, REPLACE
operations).

OTHER OPTIONS

The following additional options can be specified:

-v, --verbose

Verbose output. This option makes the list command show the interface
name, the rule options (if any), and the TOS masks. The packet and
byte counters are also listed, with the suffix 'K', 'M' or 'G' for
1000, 1,000,000 and 1,000,000,000 multipliers respectively (but see
the -x flag to change this).
For appending, insertion, deletion and replacement, this causes
detailed information on the rule or rules to be printed. -v may be
specified multiple times to possibly emit more detailed debug statements.

-n, --numeric

Numeric output.
IP addresses and port numbers will be printed in numeric format.
By default, the program will try to display them as host names,
network names, or services (whenever applicable).

-x, --exact

Expand numbers.
Display the exact value of the packet and byte counters,
instead of only the rounded number in K's (multiples of 1000)
M's (multiples of 1000K) or G's (multiples of 1000M). This option is
only relevant for the -L command.

--line-numbers

When listing rules, add line numbers to the beginning of each rule,
corresponding to that rule's position in the chain.

--modprobe=command

When adding or inserting rules into a chain, use command
to load any necessary modules (targets, match extensions, etc).

MATCH EXTENSIONS

ip6tables can use extended packet matching modules. These are loaded
in two ways: implicitly, when -p or --protocol
is specified, or with the -m or --match
options, followed by the matching module name; after these, various
extra command line options become available, depending on the specific
module. You can specify multiple extended match modules in one line,
and you can use the -h or --help
options after the module has been specified to receive help specific
to that module.

ah

This module matches the parameters in Authentication header of IPsec packets.

[!] --ahspispi[:spi]

Matches SPI.

[!] --ahlenlength

Total length of this header in octets.

--ahres

Matches if the reserved field is filled with zero.

cluster

Allows you to deploy gateway and back-end load-sharing clusters without the
need of load-balancers.

This match requires that all the nodes see the same packets. Thus, the cluster
match decides if this node has to handle a packet given the following options:

--cluster-total-nodesnum

Set number of total nodes in cluster.

[!] --cluster-local-nodenum

Set the local node number ID.

[!] --cluster-local-nodemaskmask

Set the local node number ID mask. You can use this option instead
of --cluster-local-node.

In the case of TCP connections, pickup facility has to be disabled
to avoid marking TCP ACK packets coming in the reply direction as
valid.

echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose

comment

Allows you to add comments (up to 256 characters) to any rule.

--commentcomment

Example:

iptables -A INPUT -i eth1 -m comment --comment "my local LAN"

connbytes

Match by how many bytes or packets a connection (or one of the two
flows constituting the connection) has transferred so far, or by
average bytes per packet.

The counters are 64-bit and are thus not expected to overflow ;)

The primary use is to detect long-lived downloads and mark them to be
scheduled using a lower priority band in traffic control.

The transferred bytes per connection can also be viewed through
`conntrack -L` and accessed via ctnetlink.

NOTE that for connections which have no accounting information, the match will
always return false. The "net.netfilter.nf_conntrack_acct" sysctl flag controls
whether new connections will be byte/packet counted. Existing connection
flows will not be gaining/losing a/the accounting structure when be sysctl flag
is flipped.

[!] --connbytesfrom[:to]

match packets from a connection whose packets/bytes/average packet
size is more than FROM and less than TO bytes/packets. if TO is
omitted only FROM check is done. "!" is used to match packets not
falling in the range.

--connbytes-dir {original|reply|both}

which packets to consider

--connbytes-mode {packets|bytes|avgpkt}

whether to check the amount of packets, number of bytes transferred or
the average size (in bytes) of all packets received so far. Note that
when "both" is used together with "avgpkt", and data is going (mainly)
only in one direction (for example HTTP), the average packet size will
be about half of the actual data packets.

connlimit

Allows you to restrict the number of parallel connections to a server per
client IP address (or client address block).

--connlimit-upton

Match if the number of existing connections is below or equal n.

--connlimit-aboven

Match if the number of existing connections is above n.

--connlimit-maskprefix_length

Group hosts using the prefix length. For IPv4, this must be a number between
(including) 0 and 32. For IPv6, between 0 and 128. If not specified, the
maximum prefix length for the applicable protocol is used.

--connlimit-saddr

Apply the limit onto the source group. This is the default if
--connlimit-daddr is not specified.

dscp

This module matches the 6 bit DSCP field within the TOS field in the
IP header. DSCP has superseded TOS within the IETF.

[!] --dscpvalue

Match against a numeric (decimal or hex) value [0-63].

[!] --dscp-classclass

Match the DiffServ class. This value may be any of the
BE, EF, AFxx or CSx classes. It will then be converted
into its according numeric value.

dst

This module matches the parameters in Destination Options header

[!] --dst-lenlength

Total length of this header in octets.

--dst-optstype[:length][,type[:length]...]

numeric type of option and the length of the option data in octets.

esp

This module matches the SPIs in ESP header of IPsec packets.

[!] --espspispi[:spi]

eui64

This module matches the EUI-64 part of a stateless autoconfigured IPv6 address.
It compares the EUI-64 derived from the source MAC address in Ethernet frame
with the lower 64 bits of the IPv6 source address. But "Universal/Local"
bit is not compared. This module doesn't match other link layer frame, and
is only valid in the
PREROUTING,
INPUT
and
FORWARD
chains.

frag

This module matches the parameters in Fragment header.

[!] --fragidid[:id]

Matches the given Identification or range of it.

[!] --fraglenlength

This option cannot be used with kernel version 2.6.10 or later. The length of
Fragment header is static and this option doesn't make sense.

--fragres

Matches if the reserved fields are filled with zero.

--fragfirst

Matches on the first fragment.

--fragmore

Matches if there are more fragments.

--fraglast

Matches if this is the last fragment.

hashlimit

hashlimit uses hash buckets to express a rate limiting match (like the
limit match) for a group of connections using a single iptables
rule. Grouping can be done per-hostgroup (source and/or destination address)
and/or per-port. It gives you the ability to express "N packets per time
quantum per group" (see below for some examples).

A hash limit option (--hashlimit-upto, --hashlimit-above) and
--hashlimit-name are required.

--hashlimit-uptoamount[/second|/minute|/hour|/day]

Match if the rate is below or equal to amount/quantum. It is specified as
a number, with an optional time quantum suffix; the default is 3/hour.

--hashlimit-aboveamount[/second|/minute|/hour|/day]

Match if the rate is above amount/quantum.

--hashlimit-burstamount

Maximum initial number of packets to match: this number gets recharged by one
every time the limit specified above is not reached, up to this number; the
default is 5.

--hashlimit-mode {srcip|srcport|dstip|dstport},...

A comma-separated list of objects to take into consideration. If no
--hashlimit-mode option is given, hashlimit acts like limit, but at the
expensive of doing the hash housekeeping.

--hashlimit-srcmaskprefix

When --hashlimit-mode srcip is used, all source addresses encountered will be
grouped according to the given prefix length and the so-created subnet will be
subject to hashlimit. prefix must be between (inclusive) 0 and 32. Note
that --hashlimit-srcmask 0 is basically doing the same thing as not specifying
srcip for --hashlimit-mode, but is technically more expensive.

--hashlimit-dstmaskprefix

Like --hashlimit-srcmask, but for destination addresses.

--hashlimit-namefoo

The name for the /proc/net/ipt_hashlimit/foo entry.

--hashlimit-htable-sizebuckets

The number of buckets of the hash table

--hashlimit-htable-maxentries

Maximum entries in the hash.

--hashlimit-htable-expiremsec

After how many milliseconds do hash entries expire.

--hashlimit-htable-gcintervalmsec

How many milliseconds between garbage collection intervals.

Examples:

matching on source host

"1000 packets per second for every host in 192.168.0.0/16" =>
-s 192.168.0.0/16 --hashlimit-mode srcip --hashlimit-upto 1000/sec

matching on source port

"100 packets per second for every service of 192.168.1.1" =>
-s 192.168.1.1 --hashlimit-mode srcport --hashlimit-upto 100/sec

helper

string can be "ftp" for packets related to a ftp-session on default port.
For other ports append -portnr to the value, ie. "ftp-2121".

Same rules apply for other conntrack-helpers.

hl

This module matches the Hop Limit field in the IPv6 header.

[!] --hl-eqvalue

Matches if Hop Limit equals value.

--hl-ltvalue

Matches if Hop Limit is less than value.

--hl-gtvalue

Matches if Hop Limit is greater than value.

icmp6

This extension can be used if `--protocol ipv6-icmp' or `--protocol icmpv6' is
specified. It provides the following option:

[!] --icmpv6-typetype[/code]|typename

This allows specification of the ICMPv6 type, which can be a numeric
ICMPv6
type,
type
and
code,
or one of the ICMPv6 type names shown by the command

ip6tables -p ipv6-icmp -h

iprange

This matches on a given arbitrary range of IP addresses.

[!] --src-rangefrom[-to]

Match source IP in the specified range.

[!] --dst-rangefrom[-to]

Match destination IP in the specified range.

ipv6header

This module matches IPv6 extension headers and/or upper layer header.

--soft

Matches if the packet includes any of the headers specified with
--header.

[!] --headerheader[,header...]

Matches the packet which EXACTLY includes all specified headers. The headers
encapsulated with ESP header are out of scope.
Possible header types can be:

hop|hop-by-hop

Hop-by-Hop Options header

dst

Destination Options header

route

Routing header

frag

Fragment header

auth

Authentication header

esp

Encapsulating Security Payload header

none

No Next header which matches 59 in the 'Next Header field' of IPv6 header or
any IPv6 extension headers

proto

which matches any upper layer protocol header. A protocol name from
/etc/protocols and numeric value also allowed. The number 255 is equivalent to
proto.

ipvs

Match IPVS connection properties.

[!] --ipvs

packet belongs to an IPVS connection

Any of the following options implies --ipvs (even negated)

[!] --vprotoprotocol

VIP protocol to match; by number or name, e.g. "tcp"

[!] --vaddraddress[/mask]

VIP address to match

[!] --vportport

VIP port to match; by number or name, e.g. "http"

--vdir {ORIGINAL|REPLY}

flow direction of packet

[!] --vmethod {GATE|IPIP|MASQ}

IPVS forwarding method used

[!] --vportctlport

VIP port of the controlling connection to match, e.g. 21 for FTP

length

This module matches the length of the layer-3 payload (e.g. layer-4 packet)
of a packet against a specific value
or range of values.

[!] --lengthlength[:length]

limit

This module matches at a limited rate using a token bucket filter.
A rule using this extension will match until this limit is reached.
It can be used in combination with the
LOG
target to give limited logging, for example.

xt_limit has no negation support - you will have to use -m hashlimit !
--hashlimit rate in this case whilst omitting --hashlimit-mode.

--limitrate[/second|/minute|/hour|/day]

Maximum average matching rate: specified as a number, with an optional
`/second', `/minute', `/hour', or `/day' suffix; the default is
3/hour.

--limit-burstnumber

Maximum initial number of packets to match: this number gets
recharged by one every time the limit specified above is not reached,
up to this number; the default is 5.

mac

[!] --mac-sourceaddress

Match source MAC address. It must be of the form XX:XX:XX:XX:XX:XX.
Note that this only makes sense for packets coming from an Ethernet device
and entering the
PREROUTING,
FORWARD
or
INPUT
chains.

mark

This module matches the netfilter mark field associated with a packet
(which can be set using the
MARK
target below).

[!] --markvalue[/mask]

Matches packets with the given unsigned mark value (if a mask is
specified, this is logically ANDed with the mask before the
comparison).

mh

This extension is loaded if `--protocol ipv6-mh' or `--protocol mh' is
specified. It provides the following option:

[!] --mh-typetype[:type]

This allows specification of the Mobility Header(MH) type, which can be
a numeric MH
type,
type
or one of the MH type names shown by the command

ip6tables -p ipv6-mh -h

multiport

This module matches a set of source or destination ports. Up to 15
ports can be specified. A port range (port:port) counts as two
ports. It can only be used in conjunction with
-p tcp
or
-p udp.

[!] --source-ports,--sportsport[,port|,port:port]...

Match if the source port is one of the given ports. The flag
--sports
is a convenient alias for this option. Multiple ports or port ranges are
separated using a comma, and a port range is specified using a colon.
53,1024:65535 would therefore match ports 53 and all from 1024 through
65535.

[!] --destination-ports,--dportsport[,port|,port:port]...

Match if the destination port is one of the given ports. The flag
--dports
is a convenient alias for this option.

[!] --portsport[,port|,port:port]...

Match if either the source or destination ports are equal to one of
the given ports.

owner

This module attempts to match various characteristics of the packet creator,
for locally generated packets. This match is only valid in the OUTPUT and
POSTROUTING chains. Forwarded packets do not have any socket associated with
them. Packets from kernel threads do have a socket, but usually no owner.

[!] --uid-ownerusername

[!] --uid-owneruserid[-userid]

Matches if the packet socket's file structure (if it has one) is owned by the
given user. You may also specify a numerical UID, or an UID range.

[!] --gid-ownergroupname

[!] --gid-ownergroupid[-groupid]

Matches if the packet socket's file structure is owned by the given group.
You may also specify a numerical GID, or a GID range.

[!] --socket-exists

Matches if the packet is associated with a socket.

physdev

This module matches on the bridge port input and output devices enslaved
to a bridge device. This module is a part of the infrastructure that enables
a transparent bridging IP firewall and is only useful for kernel versions
above version 2.5.44.

[!] --physdev-inname

Name of a bridge port via which a packet is received (only for
packets entering the
INPUT,
FORWARD
and
PREROUTING
chains). If the interface name ends in a "+", then any
interface which begins with this name will match. If the packet didn't arrive
through a bridge device, this packet won't match this option, unless '!' is used.

[!] --physdev-outname

Name of a bridge port via which a packet is going to be sent (for packets
entering the
FORWARD,
OUTPUT
and
POSTROUTING
chains). If the interface name ends in a "+", then any
interface which begins with this name will match. Note that in the
nat and mangleOUTPUT
chains one cannot match on the bridge output port, however one can in the
filter OUTPUT
chain. If the packet won't leave by a bridge device or if it is yet unknown what
the output device will be, then the packet won't match this option,
unless '!' is used.

[!] --physdev-is-in

Matches if the packet has entered through a bridge interface.

[!] --physdev-is-out

Matches if the packet will leave through a bridge interface.

[!] --physdev-is-bridged

Matches if the packet is being bridged and therefore is not being routed.
This is only useful in the FORWARD and POSTROUTING chains.

pkttype

This module matches the link-layer packet type.

[!] --pkt-type {unicast|broadcast|multicast}

policy

This modules matches the policy used by IPsec for handling a packet.

--dir {in|out}

Used to select whether to match the policy used for decapsulation or the
policy that will be used for encapsulation.
in
is valid in the
PREROUTING, INPUT and FORWARD
chains,
out
is valid in the
POSTROUTING, OUTPUT and FORWARD
chains.

--pol {none|ipsec}

Matches if the packet is subject to IPsec processing. --pol none
cannot be combined with --strict.

--strict

Selects whether to match the exact policy or match if any rule of
the policy matches the given policy.

For each policy element that is to be described, one can use one or more of
the following options. When --strict is in effect, at least one must be
used per element.

[!] --reqidid

Matches the reqid of the policy rule. The reqid can be specified with
setkey(8)
using
unique:id
as level.

[!] --spispi

Matches the SPI of the SA.

[!] --proto {ah|esp|ipcomp}

Matches the encapsulation protocol.

[!] --mode {tunnel|transport}

Matches the encapsulation mode.

[!] --tunnel-srcaddr[/mask]

Matches the source end-point address of a tunnel mode SA.
Only valid with --mode tunnel.

[!] --tunnel-dstaddr[/mask]

Matches the destination end-point address of a tunnel mode SA.
Only valid with --mode tunnel.

--next

Start the next element in the policy specification. Can only be used with
--strict.

quota

Implements network quotas by decrementing a byte counter with each
packet. The condition matches until the byte counter reaches zero. Behavior
is reversed with negation (i.e. the condition does not match until the
byte counter reaches zero).

[!] --quotabytes

The quota in bytes.

rateest

The rate estimator can match on estimated rates as collected by the RATEEST
target. It supports matching on absolute bps/pps values, comparing two rate
estimators and matching on the difference between two rate estimators.

For a better understanding of the available options, these are all possible
combinations:

*

rateestoperatorrateest-bps

*

rateestoperatorrateest-pps

*

(rateest minus rateest-bps1) operatorrateest-bps2

*

(rateest minus rateest-pps1) operatorrateest-pps2

*

rateest1operatorrateest2rateest-bps(without rate!)

*

rateest1operatorrateest2rateest-pps(without rate!)

*

(rateest1 minus rateest-bps1) operator
(rateest2 minus rateest-bps2)

*

(rateest1 minus rateest-pps1) operator
(rateest2 minus rateest-pps2)

--rateest-delta

For each estimator (either absolute or relative mode), calculate the difference
between the estimator-determined flow rate and the static value chosen with the
BPS/PPS options. If the flow rate is higher than the specified BPS/PPS, 0 will
be used instead of a negative value. In other words, "max(0, rateest#_rate -
rateest#_bps)" is used.

[!] --rateest-lt

Match if rate is less than given rate/estimator.

[!] --rateest-gt

Match if rate is greater than given rate/estimator.

[!] --rateest-eq

Match if rate is equal to given rate/estimator.

In the so-called "absolute mode", only one rate estimator is used and compared
against a static value, while in "relative mode", two rate estimators are
compared against another.

--rateestname

Name of the one rate estimator for absolute mode.

--rateest1name

--rateest2name

The names of the two rate estimators for relative mode.

--rateest-bps [value]

--rateest-pps [value]

--rateest-bps1 [value]

--rateest-bps2 [value]

--rateest-pps1 [value]

--rateest-pps2 [value]

Compare the estimator(s) by bytes or packets per second, and compare against
the chosen value. See the above bullet list for which option is to be used in
which case. A unit suffix may be used - available ones are: bit, [kmgt]bit,
[KMGT]ibit, Bps, [KMGT]Bps, [KMGT]iBps.

Example: This is what can be used to route outgoing data connections from an
FTP server over two lines based on the available bandwidth at the time the data
connection was started:

recent

Allows you to dynamically create a list of IP addresses and then match against
that list in a few different ways.

For example, you can create a "badguy" list out of people attempting to connect
to port 139 on your firewall and then DROP all future packets from them without
considering them.

--set, --rcheck, --update and --remove are
mutually exclusive.

--namename

Specify the list to use for the commands. If no name is given then
DEFAULT will be used.

[!] --set

This will add the source address of the packet to the list. If the source
address is already in the list, this will update the existing entry. This will
always return success (or failure if ! is passed in).

--rsource

Match/save the source address of each packet in the recent list table. This
is the default.

--rdest

Match/save the destination address of each packet in the recent list table.

[!] --rcheck

Check if the source address of the packet is currently in the list.

[!] --update

Like --rcheck, except it will update the "last seen" timestamp if it
matches.

[!] --remove

Check if the source address of the packet is currently in the list and if so
that address will be removed from the list and the rule will return true. If
the address is not found, false is returned.

--secondsseconds

This option must be used in conjunction with one of --rcheck or
--update. When used, this will narrow the match to only happen when the
address is in the list and was seen within the last given number of seconds.

--hitcounthits

This option must be used in conjunction with one of --rcheck or
--update. When used, this will narrow the match to only happen when the
address is in the list and packets had been received greater than or equal to
the given value. This option may be used along with --seconds to create
an even narrower match requiring a certain number of hits within a specific
time frame. The maximum value for the hitcount parameter is given by the
"ip_pkt_list_tot" parameter of the xt_recent kernel module. Exceeding this
value on the command line will cause the rule to be rejected.

--rttl

This option may only be used in conjunction with one of --rcheck or
--update. When used, this will narrow the match to only happen when the
address is in the list and the TTL of the current packet matches that of the
packet which hit the --set rule. This may be useful if you have problems
with people faking their source address in order to DoS you via this module by
disallowing others access to your site by sending bogus packets to you.

set

where flags are the comma separated list of
src
and/or
dst
specifications and there can be no more than six of them. Hence the command

iptables -A FORWARD -m set --match-set test src,dst

will match packets, for which (if the set type is ipportmap) the source
address and destination port pair can be found in the specified set. If
the set type of the specified set is single dimension (for example ipmap),
then the command will match packets for which the source address can be
found in the specified set.

The option --match-set can be replaced by --set if that does
not clash with an option of other extensions.

Use of -m set requires that ipset kernel support is provided, which, for
standard kernels, is the case since Linux 2.6.39.

socket

This matches if an open socket can be found by doing a socket lookup on the
packet.

--transparent

Ignore non-transparent sockets.

state

This module, when combined with connection tracking, allows access to
the connection tracking state for this packet.

[!] --statestate

Where state is a comma separated list of the connection states to
match. Possible states are
INVALID
meaning that the packet could not be identified for some reason which
includes running out of memory and ICMP errors which don't correspond to any
known connection,
ESTABLISHED
meaning that the packet is associated with a connection which has seen
packets in both directions,
NEW
meaning that the packet has started a new connection, or otherwise
associated with a connection which has not seen packets in both
directions, and
RELATED
meaning that the packet is starting a new connection, but is
associated with an existing connection, such as an FTP data transfer,
or an ICMP error.
UNTRACKED
meaning that the packet is not tracked at all, which happens if you use
the NOTRACK target in raw table.

statistic

This module matches packets based on some statistic condition.
It supports two distinct modes settable with the
--mode
option.

Supported options:

--modemode

Set the matching mode of the matching rule, supported modes are
random
and
nth.

[!] --probabilityp

Set the probability for a packet to be randomly matched. It only works with the
random mode. p must be within 0.0 and 1.0. The supported
granularity is in 1/2147483648th increments.

[!] --everyn

Match one packet every nth packet. It works only with the
nth
mode (see also the
--packet
option).

Set the offset from which it starts looking for any matching. If not passed, default is 0.

--tooffset

Set the offset up to which should be scanned. That is, byte offset-1
(counting from 0) is the last one that is scanned.
If not passed, default is the packet size.

[!] --stringpattern

Matches the given pattern.

[!] --hex-stringpattern

Matches the given pattern in hex notation.

tcp

These extensions can be used if `--protocol tcp' is specified. It
provides the following options:

[!] --source-port,--sportport[:port]

Source port or port range specification. This can either be a service
name or a port number. An inclusive range can also be specified,
using the format first:last.
If the first port is omitted, "0" is assumed; if the last is omitted,
"65535" is assumed.
If the first port is greater than the second one they will be swapped.
The flag
--sport
is a convenient alias for this option.

[!] --destination-port,--dportport[:port]

Destination port or port range specification. The flag
--dport
is a convenient alias for this option.

[!] --tcp-flagsmaskcomp

Match when the TCP flags are as specified. The first argument mask is the
flags which we should examine, written as a comma-separated list, and
the second argument comp is a comma-separated list of flags which must be
set. Flags are:
SYN ACK FIN RST URG PSH ALL NONE.
Hence the command

iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN

will only match packets with the SYN flag set, and the ACK, FIN and
RST flags unset.

[!] --syn

Only match TCP packets with the SYN bit set and the ACK,RST and FIN bits
cleared. Such packets are used to request TCP connection initiation;
for example, blocking such packets coming in an interface will prevent
incoming TCP connections, but outgoing TCP connections will be
unaffected.
It is equivalent to --tcp-flags SYN,RST,ACK,FIN SYN.
If the "!" flag precedes the "--syn", the sense of the
option is inverted.

[!] --tcp-optionnumber

Match if TCP option set.

tcpmss

This matches the TCP MSS (maximum segment size) field of the TCP header. You can only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP handshake at connection startup time.

[!] --mssvalue[:value]

Match a given TCP MSS value or range.

time

This matches if the packet arrival time/date is within a given range. All
options are optional, but are ANDed when specified. All times are interpreted
as UTC by default.

--datestartYYYY[-MM[-DD[Thh[:mm[:ss]]]]]

--datestopYYYY[-MM[-DD[Thh[:mm[:ss]]]]]

Only match during the given time, which must be in ISO 8601 "T" notation.
The possible time range is 1970-01-01T00:00:00 to 2038-01-19T04:17:07.

If --datestart or --datestop are not specified, it will default to 1970-01-01
and 2038-01-19, respectively.

--timestarthh:mm[:ss]

--timestophh:mm[:ss]

Only match during the given daytime. The possible time range is 00:00:00 to
23:59:59. Leading zeroes are allowed (e.g. "06:03") and correctly interpreted
as base-10.

[!] --monthdaysday[,day...]

Only match on the given days of the month. Possible values are 1
to 31. Note that specifying 31 will of course not match
on months which do not have a 31st day; the same goes for 28- or 29-day
February.

[!] --weekdaysday[,day...]

Only match on the given weekdays. Possible values are Mon, Tue,
Wed, Thu, Fri, Sat, Sun, or values from 1
to 7, respectively. You may also use two-character variants (Mo,
Tu, etc.).

--kerneltz

Use the kernel timezone instead of UTC to determine whether a packet meets the
time regulations.

About kernel timezones: Linux keeps the system time in UTC, and always does so.
On boot, system time is initialized from a referential time source. Where this
time source has no timezone information, such as the x86 CMOS RTC, UTC will be
assumed. If the time source is however not in UTC, userspace should provide the
correct system time and timezone to the kernel once it has the information.

Local time is a feature on top of the (timezone independent) system time. Each
process has its own idea of local time, specified via the TZ environment
variable. The kernel also has its own timezone offset variable. The TZ
userspace environment variable specifies how the UTC-based system time is
displayed, e.g. when you run date(1), or what you see on your desktop clock.
The TZ string may resolve to different offsets at different dates, which is
what enables the automatic time-jumping in userspace. when DST changes. The
kernel's timezone offset variable is used when it has to convert between
non-UTC sources, such as FAT filesystems, to UTC (since the latter is what the
rest of the system uses).

The caveat with the kernel timezone is that Linux distributions may ignore to
set the kernel timezone, and instead only set the system time. Even if a
particular distribution does set the timezone at boot, it is usually does not
keep the kernel timezone offset - which is what changes on DST - up to date.
ntpd will not touch the kernel timezone, so running it will not resolve the
issue. As such, one may encounter a timezone that is always +0000, or one that
is wrong half of the time of the year. As such, using --kerneltz is highly
discouraged.

EXAMPLES. To match on weekends, use:

-m time --weekdays Sa,Su

Or, to match (once) on a national holiday block:

-m time --datestart 2007-12-24 --datestop 2007-12-27

Since the stop time is actually inclusive, you would need the following stop
time to not match the first second of the new day:

-m time --datestart 2007-01-01T17:00 --datestop 2007-01-01T23:59:59

During lunch hour:

-m time --timestart 12:30 --timestop 13:30

The fourth Friday in the month:

-m time --weekdays Fr --monthdays 22,23,24,25,26,27,28

(Note that this exploits a certain mathematical property. It is not possible to
say "fourth Thursday OR fourth Friday" in one rule. It is possible with
multiple rules, though.)

tos

This module matches the 8-bit Type of Service field in the IPv4 header (i.e.
including the "Precedence" bits) or the (also 8-bit) Priority field in the IPv6
header.

[!] --tosvalue[/mask]

Matches packets with the given TOS mark value. If a mask is specified, it is
logically ANDed with the TOS mark before the comparison.

[!] --tossymbol

You can specify a symbolic name when using the tos match for IPv4. The list of
recognized TOS names can be obtained by calling iptables with -m tos -h.
Note that this implies a mask of 0x3F, i.e. all but the ECN bits.

u32

U32 tests whether quantities of up to 4 bytes extracted from a packet have
specified values. The specification of what to extract is general enough to
find data at given offsets from tcp headers or payloads.

[!] --u32tests

The argument amounts to a program in a small language described below.

tests := location "=" value | tests "&&" location "=" value

value := range | value "," range

range := number | number ":" number

a single number, n, is interpreted the same as n:n. n:m is
interpreted as the range of numbers >=n and <=m.

location := number | location operator number

operator := "&" | "<<" | ">>" | "@"

The operators &, <<, >> and && mean the same as in C.
The = is really a set membership operator and the value syntax describes
a set. The @ operator is what allows moving to the next header and is
described further below.

There are currently some artificial implementation limits on the size of the
tests:

*

no more than 10 of "=" (and 9 "&&"s) in the u32 argument

*

no more than 10 ranges (and 9 commas) per value

*

no more than 10 numbers (and 9 operators) per location

To describe the meaning of location, imagine the following machine that
interprets it. There are three registers:

A is of type char *, initially the address of the IP header

B and C are unsigned 32 bit integers, initially zero

The instructions are:

number B = number;

C = (*(A+B)<<24) + (*(A+B+1)<<16) + (*(A+B+2)<<8) + *(A+B+3)

&number C = C & number

<< number C = C << number

>> number C = C >> number

@number A = A + C; then do the instruction number

Any access of memory outside [skb->data,skb->end] causes the match to fail.
Otherwise the result of the computation is the final value of C.

Whitespace is allowed but not required in the tests. However, the characters
that do occur there are likely to require shell quoting, so it is a good idea
to enclose the arguments in quotes.

Example:

match IP packets with total length >= 256

The IP header contains a total length field in bytes 2-3.

--u32 "0 & 0xFFFF = 0x100:0xFFFF"

read bytes 0-3

AND that with 0xFFFF (giving bytes 2-3), and test whether that is in the range
[0x100:0xFFFF]

Example: (more realistic, hence more complicated)

match ICMP packets with icmp type 0

First test that it is an ICMP packet, true iff byte 9 (protocol) = 1

--u32 "6 & 0xFF = 1 && ...

read bytes 6-9, use & to throw away bytes 6-8 and compare the result to
1. Next test that it is not a fragment. (If so, it might be part of such a
packet but we cannot always tell.) N.B.: This test is generally needed if you
want to match anything beyond the IP header. The last 6 bits of byte 6 and all
of byte 7 are 0 iff this is a complete packet (not a fragment). Alternatively,
you can allow first fragments by only testing the last 5 bits of byte 6.

... 4 & 0x3FFF = 0 && ...

Last test: the first byte past the IP header (the type) is 0. This is where we
have to use the @syntax. The length of the IP header (IHL) in 32 bit words is
stored in the right half of byte 0 of the IP header itself.

... 0 >> 22 & 0x3C @ 0 >> 24 = 0"

The first 0 means read bytes 0-3, >>22 means shift that 22 bits to the
right. Shifting 24 bits would give the first byte, so only 22 bits is four
times that plus a few more bits. &3C then eliminates the two extra bits
on the right and the first four bits of the first byte. For instance, if IHL=5,
then the IP header is 20 (4 x 5) bytes long. In this case, bytes 0-1 are (in
binary) xxxx0101 yyzzzzzz, >>22 gives the 10 bit value xxxx0101yy and
&3C gives 010100. @ means to use this number as a new offset into
the packet, and read four bytes starting from there. This is the first 4 bytes
of the ICMP payload, of which byte 0 is the ICMP type. Therefore, we simply
shift the value 24 to the right to throw out all but the first byte and compare
the result with 0.

Example:

TCP payload bytes 8-12 is any of 1, 2, 5 or 8

First we test that the packet is a tcp packet (similar to ICMP).

--u32 "6 & 0xFF = 6 && ...

Next, test that it is not a fragment (same as above).

... 0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 = 1,2,5,8"

0>>22&3C as above computes the number of bytes in the IP header. @
makes this the new offset into the packet, which is the start of the TCP
header. The length of the TCP header (again in 32 bit words) is the left half
of byte 12 of the TCP header. The 12>>26&3C computes this length in bytes
(similar to the IP header before). "@" makes this the new offset, which is the
start of the TCP payload. Finally, 8 reads bytes 8-12 of the payload and
= checks whether the result is any of 1, 2, 5 or 8.

udp

These extensions can be used if `--protocol udp' is specified. It
provides the following options:

[!] --source-port,--sportport[:port]

Source port or port range specification.
See the description of the
--source-port
option of the TCP extension for details.

[!] --destination-port,--dportport[:port]

Destination port or port range specification.
See the description of the
--destination-port
option of the TCP extension for details.

TARGET EXTENSIONS

ip6tables can use extended target modules: the following are included
in the standard distribution.

AUDIT

This target allows to create audit records for packets hitting the target.
It can be used to record accepted, dropped, and rejected packets. See
auditd(8) for additional details.

--type {accept|drop|reject}

Set type of audit record.

Example:

iptables -N AUDIT_DROP

iptables -A AUDIT_DROP -j AUDIT --type drop

iptables -A AUDIT_DROP -j DROP

CHECKSUM

This target allows to selectively work around broken/old applications.
It can only be used in the mangle table.

--checksum-fill

Compute and fill in the checksum in a packet that lacks a checksum.
This is particularly useful, if you need to work around old applications
such as dhcp clients, that do not work well with checksum offloads,
but don't want to disable checksum offload in your device.

CLASSIFY

This module allows you to set the skb->priority value (and thus classify the packet into a specific CBQ class).

--set-classmajor:minor

Set the major and minor class value. The values are always interpreted as
hexadecimal even if no 0x prefix is given.

CONNMARK

This module sets the netfilter mark value associated with a connection. The
mark is 32 bits wide.

--set-xmarkvalue[/mask]

Zero out the bits given by mask and XOR value into the ctmark.

--save-mark [--nfmasknfmask] [--ctmaskctmask]

Copy the packet mark (nfmark) to the connection mark (ctmark) using the given
masks. The new nfmark value is determined as follows:

ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)

i.e. ctmask defines what bits to clear and nfmask what bits of the
nfmark to XOR into the ctmark. ctmask and nfmask default to
0xFFFFFFFF.

--restore-mark [--nfmasknfmask] [--ctmaskctmask]

Copy the connection mark (ctmark) to the packet mark (nfmark) using the given
masks. The new ctmark value is determined as follows:

nfmark = (nfmark & ~nfmask) ^ (ctmark & ctmask);

i.e. nfmask defines what bits to clear and ctmask what bits of the
ctmark to XOR into the nfmark. ctmask and nfmask default to
0xFFFFFFFF.

--restore-mark is only valid in the mangle table.

The following mnemonics are available for --set-xmark:

--and-markbits

Binary AND the ctmark with bits. (Mnemonic for --set-xmark
0/invbits, where invbits is the binary negation of bits.)

--or-markbits

Binary OR the ctmark with bits. (Mnemonic for --set-xmarkbits/bits.)

--xor-markbits

Binary XOR the ctmark with bits. (Mnemonic for --set-xmarkbits/0.)

--set-markvalue[/mask]

Set the connection mark. If a mask is specified then only those bits set in the
mask are modified.

--save-mark [--maskmask]

Copy the nfmark to the ctmark. If a mask is specified, only those bits are
copied.

--restore-mark [--maskmask]

Copy the ctmark to the nfmark. If a mask is specified, only those bits are
copied. This is only valid in the mangle table.

CONNSECMARK

This module copies security markings from packets to connections
(if unlabeled), and from connections back to packets (also only
if unlabeled). Typically used in conjunction with SECMARK, it is
valid in the
security
table (for backwards compatibility with older kernels, it is also
valid in the
mangle
table).

--save

If the packet has a security marking, copy it to the connection
if the connection is not marked.

--restore

If the packet does not have a security marking, and the connection
does, copy the security marking from the connection to the packet.

CT

The CT target allows to set parameters for a packet or its associated
connection. The target attaches a "template" connection tracking entry to
the packet, which is then used by the conntrack core when initializing
a new ct entry. This target is thus only valid in the "raw" table.

--notrack

Disables connection tracking for this packet.

--helpername

Use the helper identified by name for the connection. This is more
flexible than loading the conntrack helper modules with preset ports.

Assign this packet to zone id and only have lookups done in that zone.
By default, packets have zone 0.

DSCP

This target allows to alter the value of the DSCP bits within the TOS
header of the IPv4 packet. As this manipulates a packet, it can only
be used in the mangle table.

--set-dscpvalue

Set the DSCP field to a numerical value (can be decimal or hex)

--set-dscp-classclass

Set the DSCP field to a DiffServ class.

HL

This is used to modify the Hop Limit field in IPv6 header. The Hop Limit field
is similar to what is known as TTL value in IPv4. Setting or incrementing the
Hop Limit field can potentially be very dangerous, so it should be avoided at
any cost. This target is only valid in
mangle
table.

Don't ever set or increment the value on packets that leave your local network!

--hl-setvalue

Set the Hop Limit to `value'.

--hl-decvalue

Decrement the Hop Limit `value' times.

--hl-incvalue

Increment the Hop Limit `value' times.

IDLETIMER

This target can be used to identify when interfaces have been idle for a
certain period of time. Timers are identified by labels and are created when
a rule is set with a new label. The rules also take a timeout value (in
seconds) as an option. If more than one rule uses the same timer label, the
timer will be restarted whenever any of the rules get a hit. One entry for
each timer is created in sysfs. This attribute contains the timer remaining
for the timer to expire. The attributes are located under the xt_idletimer
class:

/sys/class/xt_idletimer/timers/<label>

When the timer expires, the target module sends a sysfs notification to the
userspace, which can then decide what to do (eg. disconnect to save power).

--timeoutamount

This is the time in seconds that will trigger the notification.

--labelstring

This is a unique identifier for the timer. The maximum length for the
label string is 27 characters.

LOG

Turn on kernel logging of matching packets. When this option is set
for a rule, the Linux kernel will print some information on all
matching packets (like most IPv6 IPv6-header fields) via the kernel log
(where it can be read with
dmesg
or
syslogd(8)).
This is a "non-terminating target", i.e. rule traversal continues at
the next rule. So if you want to LOG the packets you refuse, use two
separate rules with the same matching criteria, first using target LOG
then DROP (or REJECT).

Prefix log messages with the specified prefix; up to 29 letters long,
and useful for distinguishing messages in the logs.

--log-tcp-sequence

Log TCP sequence numbers. This is a security risk if the log is
readable by users.

--log-tcp-options

Log options from the TCP packet header.

--log-ip-options

Log options from the IPv6 packet header.

--log-uid

Log the userid of the process which generated the packet.

MARK

This target is used to set the Netfilter mark value associated with the packet.
It can, for example, be used in conjunction with routing based on fwmark (needs
iproute2). If you plan on doing so, note that the mark needs to be set in the
PREROUTING chain of the mangle table to affect routing.
The mark field is 32 bits wide.

--set-xmarkvalue[/mask]

Zeroes out the bits given by mask and XORs value into the packet
mark ("nfmark"). If mask is omitted, 0xFFFFFFFF is assumed.

--set-markvalue[/mask]

Zeroes out the bits given by mask and ORs value into the packet
mark. If mask is omitted, 0xFFFFFFFF is assumed.

The following mnemonics are available:

--and-markbits

Binary AND the nfmark with bits. (Mnemonic for --set-xmark
0/invbits, where invbits is the binary negation of bits.)

--or-markbits

Binary OR the nfmark with bits. (Mnemonic for --set-xmarkbits/bits.)

--xor-markbits

Binary XOR the nfmark with bits. (Mnemonic for --set-xmarkbits/0.)

NFLOG

This target provides logging of matching packets. When this target is
set for a rule, the Linux kernel will pass the packet to the loaded
logging backend to log the packet. This is usually used in combination
with nfnetlink_log as logging backend, which will multicast the packet
through a
netlink
socket to the specified multicast group. One or more userspace processes
may subscribe to the group to receive the packets. Like LOG, this is a
non-terminating target, i.e. rule traversal continues at the next rule.

--nflog-groupnlgroup

The netlink group (0 - 2^16-1) to which packets are (only applicable for
nfnetlink_log). The default value is 0.

--nflog-prefixprefix

A prefix string to include in the log message, up to 64 characters
long, useful for distinguishing messages in the logs.

--nflog-rangesize

The number of bytes to be copied to userspace (only applicable for
nfnetlink_log). nfnetlink_log instances may specify their own
range, this option overrides it.

--nflog-thresholdsize

Number of packets to queue inside the kernel before sending them
to userspace (only applicable for nfnetlink_log). Higher values
result in less overhead per packet, but increase delay until the
packets reach userspace. The default value is 1.
.SSNFQUEUE
This target is an extension of the QUEUE target. As opposed to QUEUE, it allows
you to put a packet into any specific queue, identified by its 16-bit queue
number.
It can only be used with Kernel versions 2.6.14 or later, since it requires
the
nfnetlink_queue
kernel support. The queue-balance option was added in Linux 2.6.31,
queue-bypass in 2.6.39.

--queue-numvalue

This specifies the QUEUE number to use. Valid queue numbers are 0 to 65535. The default value is 0.

--queue-balancevalue:value

This specifies a range of queues to use. Packets are then balanced across the given queues.
This is useful for multicore systems: start multiple instances of the userspace program on
queues x, x+1, .. x+n and use "--queue-balance x:x+n".
Packets belonging to the same connection are put into the same nfqueue.

--queue-bypass

By default, if no userspace program is listening on an NFQUEUE, then all packets that are to be queued
are dropped. When this option is used, the NFQUEUE rule is silently bypassed instead. The packet
will move on to the next rule.

NOTRACK

This target disables connection tracking for all packets matching that rule.

It can only be used in the
raw
table.

RATEEST

The RATEEST target collects statistics, performs rate estimation calculation
and saves the results for later evaluation using the rateest match.

--rateest-namename

Count matched packets into the pool referred to by name, which is freely
choosable.

--rateest-intervalamount{s|ms|us}

Rate measurement interval, in seconds, milliseconds or microseconds.

--rateest-ewmalogvalue

Rate measurement averaging time constant.

REJECT

This is used to send back an error packet in response to the matched
packet: otherwise it is equivalent to
DROP
so it is a terminating TARGET, ending rule traversal.
This target is only valid in the
INPUT,
FORWARD
and
OUTPUT
chains, and user-defined chains which are only called from those
chains. The following option controls the nature of the error packet
returned:

--reject-withtype

The type given can be
icmp6-no-route,
no-route,
icmp6-adm-prohibited,
adm-prohibited,
icmp6-addr-unreachable,
addr-unreach,
icmp6-port-unreachable or
port-unreach
which return the appropriate ICMPv6 error message (port-unreach is
the default). Finally, the option
tcp-reset
can be used on rules which only match the TCP protocol: this causes a
TCP RST packet to be sent back. This is mainly useful for blocking
ident
(113/tcp) probes which frequently occur when sending mail to broken mail
hosts (which won't accept your mail otherwise).
tcp-reset
can only be used with kernel versions 2.6.14 or later.

SECMARK

This is used to set the security mark value associated with the
packet for use by security subsystems such as SELinux. It is
valid in the
security
table (for backwards compatibility with older kernels, it is also
valid in the
mangle
table). The mark is 32 bits wide.

--selctxsecurity_context

SET

This modules adds and/or deletes entries from IP sets which can be defined
by ipset(8).

--add-setsetnameflag[,flag...]

add the address(es)/port(s) of the packet to the sets

--del-setsetnameflag[,flag...]

delete the address(es)/port(s) of the packet from the sets

where flags are
src
and/or
dst
specifications and there can be no more than six of them.

--timeoutvalue

when adding entry, the timeout value to use instead of the default
one from the set definition

--exist

when adding entry if it already exists, reset the timeout value
to the specified one or to the default from the set definition

Use of -j SET requires that ipset kernel support is provided, which, for
standard kernels, is the case since Linux 2.6.39.

TCPMSS

This target allows to alter the MSS value of TCP SYN packets, to control
the maximum size for that connection (usually limiting it to your
outgoing interface's MTU minus 40 for IPv4 or 60 for IPv6, respectively).
Of course, it can only be used
in conjunction with
-p tcp.

This target is used to overcome criminally braindead ISPs or servers
which block "ICMP Fragmentation Needed" or "ICMPv6 Packet Too Big"
packets. The symptoms of this
problem are that everything works fine from your Linux
firewall/router, but machines behind it can never exchange large
packets:

1.

Web browsers connect, then hang with no data received.

2.

Small mail works fine, but large emails hang.

3.

ssh works fine, but scp hangs after initial handshaking.

Workaround: activate this option and add a rule to your firewall
configuration like:

Explicitly sets MSS option to specified value. If the MSS of the packet is
already lower than value, it will not be increased (from Linux
2.6.25 onwards) to avoid more problems with hosts relying on a proper MSS.

--clamp-mss-to-pmtu

Automatically clamp MSS value to (path_MTU - 40 for IPv4; -60 for IPv6).
This may not function as desired where asymmetric routes with differing
path MTU exist --- the kernel uses the path MTU which it would use to send
packets from itself to the source and destination IP addresses. Prior to
Linux 2.6.25, only the path MTU to the destination IP address was
considered by this option; subsequent kernels also consider the path MTU
to the source IP address.

These options are mutually exclusive.

TCPOPTSTRIP

This target will strip TCP options off a TCP packet. (It will actually replace
them by NO-OPs.) As such, you will need to add the -p tcp parameters.

--strip-optionsoption[,option...]

Strip the given option(s). The options may be specified by TCP option number or
by symbolic name. The list of recognized options can be obtained by calling
iptables with -j TCPOPTSTRIP -h.

TEE

The TEE target will clone a packet and redirect this clone to another
machine on the local network segment. In other words, the nexthop
must be the target, or you will have to configure the nexthop to forward it
further if so desired.

--gatewayipaddr

Send the cloned packet to the host reachable at the given IP address.
Use of 0.0.0.0 (for IPv4 packets) or :: (IPv6) is invalid.

To forward all incoming traffic on eth0 to an Network Layer logging box:

-t mangle -A PREROUTING -i eth0 -j TEE --gateway 2001:db8::1

TOS

This module sets the Type of Service field in the IPv4 header (including the
"precedence" bits) or the Priority field in the IPv6 header. Note that TOS
shares the same bits as DSCP and ECN. The TOS target is only valid in the
mangle table.

--set-tosvalue[/mask]

Zeroes out the bits given by mask (see NOTE below) and XORs value
into the TOS/Priority field. If mask is omitted, 0xFF is assumed.

--set-tossymbol

You can specify a symbolic name when using the TOS target for IPv4. It implies
a mask of 0xFF (see NOTE below). The list of recognized TOS names can be
obtained by calling iptables with -j TOS -h.

The following mnemonics are available:

--and-tosbits

Binary AND the TOS value with bits. (Mnemonic for --set-tos
0/invbits, where invbits is the binary negation of bits.
See NOTE below.)

--or-tosbits

Binary OR the TOS value with bits. (Mnemonic for --set-tosbits/bits. See NOTE below.)

--xor-tosbits

Binary XOR the TOS value with bits. (Mnemonic for --set-tosbits/0. See NOTE below.)

NOTE: In Linux kernels up to and including 2.6.38, with the exception of
longterm releases 2.6.32 (>=.42), 2.6.33 (>=.15), and 2.6.35 (>=.14), there is
a bug whereby IPv6 TOS mangling does not behave as documented and differs from
the IPv4 version. The TOS mask indicates the bits one wants to zero out, so it
needs to be inverted before applying it to the original TOS field. However, the
aformentioned kernels forgo the inversion which breaks --set-tos and its
mnemonics.

TPROXY

This target is only valid in the mangle table, in the PREROUTING
chain and user-defined chains which are only called from this chain. It
redirects the packet to a local socket without changing the packet header in
any way. It can also change the mark value which can then be used in advanced
routing rules.
It takes three options:

--on-portport

This specifies a destination port to use. It is a required option, 0 means the
new destination port is the same as the original. This is only valid if the
rule also specifies -p tcp or -p udp.

--on-ipaddress

This specifies a destination address to use. By default the address is the IP
address of the incoming interface. This is only valid if the rule also
specifies -p tcp or -p udp.

--tproxy-markvalue[/mask]

Marks packets with the given value/mask. The fwmark value set here can be used
by advanced routing. (Required for transparent proxying to work: otherwise
these packets will get forwarded, which is probably not what you want.)

TRACE

This target marks packets so that the kernel will log every rule which match
the packets as those traverse the tables, chains, rules.

A logging backend, such as ip(6)t_LOG or nfnetlink_log, must be loaded for this
to be visible.
The packets are logged with the string prefix:
"TRACE: tablename:chainname:type:rulenum " where type can be "rule" for
plain rule, "return" for implicit rule at the end of a user defined chain
and "policy" for the policy of the built in chains.
It can only be used in the
raw
table.

DIAGNOSTICS

Various error messages are printed to standard error. The exit code
is 0 for correct functioning. Errors which appear to be caused by
invalid or abused command line parameters cause an exit code of 2, and
other errors cause an exit code of 1.

BUGS

Bugs? What's this? ;-)
Well... the counters are not reliable on sparc64.

COMPATIBILITY WITH IPCHAINS

This ip6tables
is very similar to ipchains by Rusty Russell. The main difference is
that the chains INPUT and OUTPUT
are only traversed for packets coming into the local host and
originating from the local host respectively. Hence every packet only
passes through one of the three chains (except loopback traffic, which
involves both INPUT and OUTPUT chains); previously a forwarded packet
would pass through all three.

The other main difference is that -i refers to the input interface;
-o refers to the output interface, and both are available for packets
entering the FORWARD chain.
There are several other changes in ip6tables.

SEE ALSO

The packet-filtering-HOWTO details iptables usage for
packet filtering,
the netfilter-extensions-HOWTO details the extensions that are
not in the standard distribution,
and the netfilter-hacking-HOWTO details the netfilter internals.
See
http://www.netfilter.org/.

AUTHORS

Rusty Russell wrote iptables, in early consultation with Michael
Neuling.

Marc Boucher made Rusty abandon ipnatctl by lobbying for a generic packet
selection framework in iptables, then wrote the mangle table, the owner match,
the mark stuff, and ran around doing cool stuff everywhere.

James Morris wrote the TOS target, and tos match.

Jozsef Kadlecsik wrote the REJECT target.

Harald Welte wrote the ULOG and NFQUEUE target, the new libiptc, as well as TTL match+target and libipulog.